1. Field of the Invention
This invention concerns an improved process for producing chlorine and iron oxide from iron chlorides. More particularly, it concerns such a process wherein the ferric chloride is treated in the vapor phase with oxygen in a fluidized-bed reactor.
2. Prior Art
Several industrial processes, such as the direct chlorination of ilmenite ores to produce titania, generate large quantities of by-product iron chlorides. Disposal of these iron chlorides poses potential pollution problems and represents an economic loss for the chlorine content of the by-products.
Harris, et al, "Process for Chlorination of Titanium Bearing Materials and for Dechlorination of Iron Chloride", in World Mining and Metals Technology, Alfred Weiss, Ed., The Society of Mining Engineers, New York, Chapter 44, pages 693-712 (August 1976), suggest that ferric chloride can be treated with oxygen in a fluidized-bed reactor in the vapor phase. The process produces chlorine gas, which can be recycled to an ilmenite chlorination process, and iron oxide by-product rather than soluble chloride wastes. According to Harris et al, the process, which was investigated on laboratory size equipment at temperatures of 500.degree. to 550.degree. C., includes: feeding preheated oxygen into the bottom of the reactor countercurrent to product iron oxide which exits to collection from the bottom of the reactor; feeding solid ferric chloride particles to the reactor; optionally feeding small amounts of carbon to furnish heat to the system; and treating in a separated stream a portion of the iron oxide collected with sodium chloride which may then be recycled to the reactor as a catalyst in an amount equal to about 25 percent by weight of the ferric chloride feed. Although this process is reported to operate satisfactorily on the laboratory scale, the authors point out that an industrial process for waste conversion of ferric chloride by dechlorination is still needed.
Others, such as Sawyer, U.S. Pat. No. 2,642,339, describe similar ferric chloride treatments in the vapor phase with oxygen in fluidized-bed reactors, but these processes do not suggest the use of supplementary fuel in the reactor. Dunn et al, U.S. Pat. No. 3,376,112, disclose carrying out the dechlorination reaction in a moving bed reactor wherein carbon-containing fuel materials, such as carbon tetrachloride, carbon monoxide, phosgene or hydrocarbons, optionally may be used. In still another process for treating iron chloride in the vapor phase with oxygen, Nelson et al, U.S. Pat. No. 3,092,456, disclose the use of a once-through, vapor-phase combustion chamber, wherein iron oxide incrustations on the walls of apparatus downstream of the combustion chamber can be prevented by deactivating the oxygen in the reaction product stream by introducing into the product stream, at a point downstream of the reaction zone, a material such as hydrogen, ammonia, methane, producer gas, benzene, diethyl ether, acetone, carbon monoxide, or finely ground metallurgical coke.
Although each of the above described processes has shown some promise for industrial application, it has been found that for highest conversion of iron chloride to chlorine and iron oxide on an industrial scale, a recirculating-fluidized-bed reactor, for example of the type suggested by Reeves et al, U.S. Pat. No. 3,793,444, is preferred. Reeves et al suggest that it is generally unnecessary, at least in a commercial size operation, to supply heat directly to the system once a steady state is achieved. However, it has now been found that in industrial scale equipment of this type, control of temperature, especially during variations in ferric chloride feed rates, is most difficult and can often lead to uncontrolled temperature excursions.
To overcome the problems associated with uncontrolled temperature excursions in recirculating-fluidized-bed reactors, the present invention provides for the addition of particulate solid carbonaceous fuels. It was surprising that only certain specific fuels were satisfactory in overcoming these temperature problems associated with ferric chloride dechlorination reactions in industrial size recirculating-fluidized-bed reactors.